This invention was not developed in conjunction with any Federally sponsored contract.
Not applicable.
1. Field of the Invention
This invention relates to the arts of imaging, image processing, and digital displays including display design and moirxc3xa9 reduction technologies.
2. Background of the Invention
Well-known imaging technologies include film (e.g. analog), digital, and analog-digital hybrid approaches. Film imaging processes use a set of lenses to focus an image onto a film sheet which is impregnated with grains of material reactive to the spectrum to be recorded, such as visible light, infrared (xe2x80x9cIRxe2x80x9d), or X-ray. The grains are randomly arranged in each sheet of film, and thus reproduction of the image on the developed film has a certain resolution based on the size and density of these grains. To display this image, the general arrangement of FIG. 2a is employed by film projectors. If the image is a moving image, such as a feature length movie, a film (25) consisting of a plurality of individual xe2x80x9cframesxe2x80x9d or images is passed between a light source (23) and a focussing lens (24). The incident image (22) on a screen is then perceptible by an observer. For still film image reproduction, such as slides, the film (25) of this arrangement is a single frame. This arrangement can be viewed as a purely analog image reproduction process.
In digital imaging, a sensor of uniformly-arranged sensing elements is used to capture xe2x80x9cbitsxe2x80x9d or pixels of the image. The pixelated image data set is then stored in a digital file. To reproduce the image and display it to an observer, typically a two-dimensional array of uniformly-spaced display elements (10), as shown in FIG. 1, is modulated according to the data set. In this example, the display elements (11) may be light-emitting diodes (LED) or thin film transistor (TFT) as commonly used in flat panel displays and laptop computer displays, or the more recently developed organic thin-film transistor technology. The status (on/off) and apparent brightness of each display element can be controlled by a display controller, either through analog brightness control (voltage or current setting), or through pulse modulation of the display elements.
The two-dimensional array usually has a uniform spacing d1 between elements (11) in the x-axis, or horizontal direction, and a uniform spacing d2 between the elements in the y-axis, or vertical direction. For many displays, these two spacings are equal (e.g. d1=d2).
To project a digital image, many computer projectors use a transparent liquid crystal display (LCD) (27) in place of the typical analog film situated between a light source (23) and a focussing lens (24), as illustrated in FIG. 2b. This essentially a digital adaptation of the old analog film projector. A controller then drives the transparent LCD (27) controls in order to recreate the digital image on the screen (21).
A hybrid arrangement (e.g. partially analog, partially digital) which is common place is the cathode ray tube (CRT), in which horizontal xe2x80x9clinesxe2x80x9d of image are driven by analog signals, but also in which the image is broken vertically into discrete lines. FIG. 3a shows the general arrangement of well-known CRT displays, in which one or more electron guns (35) are controlled so that the resulting incident pattern on a phosphorous-treated screen (21) reproduces an image. Typically, the picture is xe2x80x9cpaintedxe2x80x9d by repetitiously scanning the electron beam (36) across the screen (21) in a side-to-side (horizontal) manner, incrementing to an adjacent row or line up or down with each scan from top to bottom.
So, over time, the x-axis or horizontal position of the electron beam incident on the screen is driven by a sawtooth or ramp function as shown in FIG. 3b, wherein each xe2x80x9crampxe2x80x9d represents a single line sweep from left to right, for example. The vertical or y-axis position of the electron beam, though, is modulated in discrete steps, such as from top-to-bottom or from bottom-to-top. As each line of the display is swept by the electron beam, the intensity or strength of the beam is modulated causing an apparent increase or decrease in the apparent brightness on the screen. One can view this type of display as being analog in the x-axis (e.g. across each line), but digital in the y-axis (e.g. vertically from line to line).
Moirxc3xa9 patterns are artifacts of certain imaging processes which are perceptible to the human eye, but do not represent actual features or details in the original item imaged. They often resemble crosshatch halftones across all or a portion of a displayed digital image.
For example, when displaying an image having a feature or line at an angle slightly off perfect horizontal or vertical, such as at a 3xc2x0 or 87xc2x0 angle on a digital screen, on a TFT laptop computer display which has equal horizontal and vertical pixel-to-pixel spacing, a moirxc3xa9 pattern may be apparent. This occurs because the pixel spacing of the display elements closely matches with image feature. If one considers the display element spacing as one xe2x80x9csignalxe2x80x9d or function, and the feature within the image as another signal or function, the moirxc3xa9 pattern can be seen as interference pattern between the two signals. As such, changing the display in harmonic manners, such as doubling the density of the display elements, does not reduce the appearance of moirxc3xa9 patterns. This is a well-known phenomena, and is experienced by viewers of all sorts of digital displays often. Even with partially digital displays, such as CRTs, features such as horizontal lines on sports fields may cause noticeable interference with the horizontal lines of the display.
The related patent applications disclosed methods and systems for avoiding the encoding of moirxc3xa9 patterns when digitally recording an image using non-uniformly spaced sensor elements. This allowed images which have features that would normally interfere or resonate with the sensor pattern of typical uniformly-spaced sensor arrays to be captured without the creation of moirxc3xa9 patterns in the data.
However, many images are only available in standard formats, such as bit maps (BMP), Joint Photographic Experts Group (JPEG), or Moving Pictures Experts Group (MPEG) formats, which are based upon uniformly spaced xe2x80x9csamplesxe2x80x9d of the original image. As the inventions of the related applications only reduced moire pattern effects in newly captured images, they are of little use in displaying digital images which were captured using traditional sensor arrays.
Therefore, there is a need in the art for a system and method of digital image display which avoids the appearance of moirxc3xa9 patterns. Further, there is a need in the art for this new system and method to be compatible with common digital image formats such as BMP, JPEG and MPEG.